1. Field of the Invention
The present invention relates to a yttrium-containing composite powder, a composite sintered body formed from such a composite powder, and a method of manufacturing such a composite powder and a composite sintered body.
2. Description of the Related Art
Sintered bodies composed mainly of silicon nitride and silicon carbide are finding wide use as various structural ceramic materials as substitutes for metallic materials because they are highly mechanically strong, highly resistant to heat, shocks, wear, and acids, and are also lightweight.
For improving mechanical characteristics, such as mechanical strength and toughness, of ceramic materials, it has been proposed to disperse silicon carbide (SIC) within particles of silicon nitride (Si.sub.3 N.sub.4). Since such ceramic materials are highly resistant to heat, mechanically strong, and have good fracture toughness, they are suitable as materials of parts which will be used under high temperature and high loads.
However, since silicon carbide has been dispersed by chemical vapor deposition (CVD), the productivity of the resultant composite ceramic materials is low. The powder of such composite ceramic materials is too fine to handle well. In addition, the composite ceramic powder has poor sinterability if only silicon carbide is dispersed within particles of silicon nitride.
A composite ceramic material has been manufactured as follows: a powder of silicon nitride, a powder of silicon carbide, and a small amount of sintering additive, such as of yttrium oxide (Y.sub.2 O.sub.3) are mixed so as to be uniformly dispersed, molded to shape, and then sintered. However, different powders cannot be uniformly dispersed beyond the limitation imposed by their particle diameters. For manufacturing a uniform composite ceramic material of silicon nitride and silicon carbide, it has been proposed to produce a composite powder composed of mixed ingredients, molding the composite powder to shape, and sintering the molded body.
According to one proposed process, polysilazane or polysilane is used as a precursor of a composite ceramic material of silicon nitride and silicon carbide, and combined with a compound of titanium, aluminum, hafnium, zirconium, or the like to produce a composite polymer, which is then sintered into a ceramic material.
For example, Japanese laid-open patent publication No. 63-191832 discloses a process of manufacturing polyaluminosilazane by reacting, with heat, polysilazane having a main skeleton composed of units represented by a general formula of -SiR.sup.1 R.sup.2 -NR.sup.3 - where R.sup.1, R.sup.2, R.sup.3 represent a hydrogen atom, an alkyl group, an alkenyl group, or the like, with at least one being a hydrogen atom, and having a number average molecular weight ranging from 100 to 50000, with aluminum alkoxide represented by a general formula of Al(OR.sup.4).sup.3 where R.sup.4 represents a hydrogen atom, an alkyl group, or aryl group. The produced polyaluminosilazane is used to synthesize a Si--Al--O--N ceramic (sialon).
Japanese laid-open patent publication No. 3-190932 discloses a process of manufacturing a ceramic by reacting a hafnium compound represented by a general formula of HfX.sub.4 where X represents a chlorine atom or a bromine atom with disilazane represented by a general formula of (SiR.sup.1 R.sup.2 R.sup.3).sub.2 NH where R.sup.1, R.sup.2, R.sup.3 represent a hydrogen atom, a methyl group, or the like and may be the same as or different from each other, thereby generating a hafnium-containing silazane polymer, melting and molding the hafnium-containing silazane polymer to shape, making the molded body infusible, and thereafter sintering the infusible molded body.
Japanese laid-open patent publication No. 3-81330 shows a process of manufacturing a polytitanocarbosilazane by reacting (A) a organic silicon compound represented by a general formula of X--SiR.sup.1.sub.2 --CHR.sup.2 --CHR.sup.2 --SiR.sup.1.sub.2 --X where R.sup.1 represents hydrogen, chlorine, bromine, a methyl group, an ethyl group, or the like, R.sup.2 represents hydrogen or a methyl group, and X represents chlorine or bromine, (B) a halogen silane compound, (C) a titanium compound, and (D) disilazane represented by a general formula of (R.sup.3.sub.3 Si).sub.2 NH where R.sup.3 represents a hydrogen atom, a methyl group, or the like.
No compound material with yttrium combined with polysilazane has been reported yet.
Japanese laid-open patent publication No. 64-66239 discloses a process using a sintering additive of yttrium. According to the disclosed process, a mixture containing organic halogen silane and a reactive metal compound including a metal such as aluminum, yttrium, or the like is treated at a temperature ranging from 100.degree. to 340.degree. C. to produce halogen-containing metal polysilane. The halogen-containing metal polysilane is reacted with an aminolysis reagent represented by a general formula of either NHR.sup.iv.sub.2 where R.sup.iv.sub.2 represents hydrogen, an alkyl group, or a phenyl group or --SiR.sup.v.sub.3 where R.sup.v is an alkyl group or the like within a suitable solvent under a waterless condition at a temperature ranging from 25.degree. to 100.degree. C. to collect metal polysilane containing R.sup.iv.sub.2 N--. A ceramic which is formed from metal polysilane containing R.sup.iv.sub.2 N-- is composed mainly of silicon carbide, and is less resistant to heat and shocks and has poorer fracture toughness than a ceramic composed mainly of silicon nitride formed from composite polysilazane.